A computed tomography (CT) scanner generally includes a rotating gantry rotatably supported by a stationary gantry. The rotating gantry is configured to rotate about an examination region and supports an x-ray tube that rotates therewith. The x-ray tube is configured to emit ionizing radiation at least in a direction towards the examination region. A source collimator collimates the radiation, producing a radiation beam, having a predetermined shape, which traverses the examination region and a portion of an object or subject in the examination region. A subject support supports the object or subject in the examination region. A detector array, located across the examination region and opposite the x-ray tube, detects radiation traversing the examination region and the object or subject and generates projection data indicative thereof. A reconstructor reconstructs the projection data and generates three dimensional volumetric image data.
Typically, before the above-discussed three dimensional volume scan of the object or subject, one or more pre-scans (e.g., surview, scout, pilot, etc. scans) are performed. For a typical pre-scan, the rotating gantry and hence the x-ray tube is rotated to, if not already at, and held or maintained at a static angular position. Then, the subject support translates the object or subject through the examination region while the x-ray tube emits radiation and the detector detects radiation. The reconstructor reconstructs a two-dimensional (2D) projection image for each pre-scan from the acquired data. The 2D projection image(s) is used to facilitate creating an imaging examination plan for the three dimensional volume scan of the object or subject. This has included using the 2D projection image to identify a region of interest (ROI), identify a start scan location, and identify an end scan location (or scan length) to scan the ROI.
By way of non-limiting example, FIGS. 1 and 2 respectively show a patient 102 and a ROI 104 in the patient 102 from a side view and a front view of the patient 102. Note that the ROI 104 is depicted as a sphere in this example. However, it is to be understood that the ROI 104 can be other geometrical shapes, including, but not limited to irregular. FIG. 3 shows an example 2D projection image 302 with anatomical structure outside of the ROI 104 visually removed from within the patient 102 for clarity of this discussion. FIG. 3 also shows an imaging plan 304 for a three dimensional volume scan of the ROI 104, including a start scan location 306 and an end scan location 308 (or a scan length 310). FIGS. 4, 5 and 6 respectively shows a radiation source 400, a collimator 402 with a fixed collimation, and a corresponding radiation beam 404 at three different view angles 406, 408, and 410 for a volume scan of the ROI 104 in the patient 102 based on the plan 304 in FIG. 3. The slice shown in FIGS. 4, 5 and 6 corresponds to a slice 106 shown in FIGS. 1, 2 and 3.
Note that in this example, the size of the ROI 104 is less than one tenth of the anatomical structure irradiated each view during the scan. Thus, the patient 102 receives substantially more dose than that needed to image the ROI 104 in each view. Unfortunately, CT scanners emit ionizing radiation, which may damage or kill cells and/or increase the risk of cancer. As such, there is an unresolved need for other approaches for scanning a ROI within a patient.